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What exactly are you modelling?
traveler_hauptman Member, OS Professional, Mentor, Developers Posts: 419 PRO
edited July 2015 in General
I often see a big disconnect between what models actually are and how people try to use them. This is true for all types of models, but here it makes sense focus in on solid models for mechanical design capture. I'm really curious about what other peoples experience has been.
A fundamental premise is that a model is an approximate representation of a real system that we use to make predictions or communicate about that system.
My assertion is that adding details to a model that don't support the goals of the model is a waste of time. This takes two forms. Details that don't support the end result (modeling internal details of an off-the-shelf part, bearing balls or grade markings on a bolt for instance). Details that are beyond the fidelity of the model such that changing the parameters of the detail has no effect on the end result. The latter is seen in simulation more often that solid modeling I think.
A discussion on how to create a knurl in Onshape got me thinking on this topic again. The OP wanted help creating a knurl and the reply created geometry that gave the appearance of a knurl. It seems that the answer satisfied the OP and everyone was happy. Everyone except me.
Traditionally a knurl is a deformation process. A tool rolls on a plastic surface forcing material out of the valleys of the pattern and onto the peaks. Which means that the knurled surface of a cylinder has a larger diameter than the starting surface.
So what would I model for a knurl? In the design phase we care about collisions and I would model the knurl as a larger diameter cylinder to capture the potential for interference with other parts, especially parts being assembled over the knurl. In a manufacturing drawing, the knurl will be a drawing note rather than dimensioned in the drawing and the lines of the knurl cylinder will give the right information in the drawing views. Finally, when user manual or marketing materials need it, I would add the visual representation of the knurl.
To be clear, are reasons, due to manufacturing process or model intent that the knurl model that sparked this could have been exactly the right model for the job.
The knurl above is just one example of differences between what a model is useful for and what we do with them.
I think this is important because as soon as the Onshape guys loose sight of the fundamentals of modeling, we start getting a bunch of features that don't serve us, at the expense of the features we need.
What do you think? What are the worst offences of useless detail you have seen? Can Onshape do something to help?